"She's suffered with special needs at school since the age of seven with dyslexia. So much so, she's combated it to get an A* in history to go to university.

"Let's focus on that shall we? Can we focus on the fact that she's a healthy size 10? This woman in particular, I would like to go to her family and look at the size of her derriere."

Ferguson then revealed that she was talking about Pearson, causing a ripple of laughter among the assembled journalists.

"I'm not saying people can't have the freedom to write what they think but they should return my calls. That's just bad manners," she added.

Pearson had written in her Daily Mail column: "I fear Bea is in danger of combining her mother's toe-curling excesses with her dad's physique. Can someone please have a kindly word with her before it all goes pear-shaped?"

One reporter at the press conference yesterday said: "Another journalist asked [Ferguson] who she was talking about. She said 'Allison Pearson'. Everyone cracked up, then the PRs from ITV swiftly tried to move her on. She was genuinely fuming."

Pearson is following in the footsteps of her legendary predecessor Lynda Lee-Potter, who caused a huge outcry when she attacked the appearance of the late Labour MP and minister Mo Mowlam.

It turned out that Mowlam was suffering from brain cancer and had undergone chemotherapy.

Lee-Potter later interviewed Mowlam. But there is no sign that Pearson and Ferguson have called time on their feud, despite the Duchess and Beatrice offering to take the Daily Mail columnist to lunch.

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